Capacitors

[dskowron]

When would you use an electrolytic and when would you use one that isn't electrolytic? Would one of each of the same value and voltage rating be interchangeable?

[Enzo]

Electrically they would be interchangable in most cases. But the size difference is enormous. An electrolytic cap of 10uf 100v rating is about the size of an eraser on the end of a pencil. A film cap of the same ratings would be many many times that size.

The electrolytic cap has the advantage of packing a high value into a small size.

Obviously we have to consider each situation, but in general, a very rough rule of thumb would be any cap over 1uf is probably going to be electrolytic, and any under 1uf will probably be a film cap. Under 1000pf - .001uf - you generally see ceramic caps or silver-mica caps. Certainly it is not hard to find exceptions to this, but I think it is a reasonable expectation.

As an experiment, look up the dimensions of a common 22uf 500v e-cap. Without looking I'd say roughly the size of a 12AX7. See what the largest 500v non-electrolytic cap you can find is and its size.

[martin manning]

Heck, a 0.1 uF 600V Sprague Orange Drop is almost that big... 200:1 difference in Volume/Capacity in round numbers!

MPM

[dskowron]

Thanks guys. I get it now.

[Diablo]

Wait a minute!
Electrolytic caps are NOT interchangeable with other caps!
They are polarized, and you need to pay attention to the negative and positive terminal. Reverse polarity on an aluminum electrolytic cap and the dielectric is destroyed and the cap shorts out and can explode. Electrolytic caps are not designed for AC. In your amp, the electrolytics are connected after some type of rectifier, to make sure they don't see reverse voltage. The rest of the caps in your amp are non-polarized and handle AC without a problem.

[Enzo]

You miss the point.

Sure e-caps have polarity, that is one of the trade-offs for their small size. But the point being made was that you can replace that polarized e-cap with a plain old non-polarized film cap.... if you can find one with the ratings AND it will even fit in your amp. Finding non-electrolytic caps to replace your basic 22uf 500v filter caps will be difficult. But if you found such caps, they would work fine.

Electrolytic caps are not designed for AC. In your amp, the electrolytics are connected after some type of rectifier, to make sure they don't see reverse voltage. The rest of the caps in your amp are non-polarized and handle AC without a problem.

Look at the output to the speaker on an old Acoustic Bass amp - the 370 for example - that single supply amp stage has its output bus sitting at +45VDC, and a large 3900uf e-cap passes the signal to the speaker. We often have threads about old transistor amps like early Peavey Mace or Deuce and of course old Vox solid state amps. We wind up recommending the amps get ALL the little small e-caps replaced. They are in the 1-5uf range, and are used as signal couplers between stages.

It is important to understand the difference between AC and signal on DC. The plate of a 12AX7 somewhere in an amp might have 30-40 volts of signal on it - we might consider that AC, but really it is just DC that varies. That plate will always be positive. If I connected an e-cap to that plate with its negative end to ground or something lower voltage like a following grid, it would never see reverse polarity. But it would pass signal.

[nopainkiller]

so it would be safe to replace ceramic, film, tant, silver-mica or box film caps with electrolytic caps. But other way around, and you gotta pay attention to polarity.

Also different kinda caps give different sounds. Try replacing a film cap with a tant cap, or a ceramic cap with a film one.

[Enzo]

You said that backwards. The e-caps have polarity, while film/ceramic/mica do not.

Not every place is a good place for an e-cap. The discussion was just about when to use one or another in the general case. In the general sense they are interchangeable. In a practical sense, sometimes the size issue alone makes it silly. And certainly when guys care and obsess over brands of film caps, they would feel even more strongly about e-cap vs film vs mica vs whatever.

And there are other practical issues. If you have a .022uf coupling film cap, where would you find a .022uf electrolytic to replace it with even if you wanted to? But if we had them , in many cases we could use them. That was what my very crude rule of thumb was - the size of the cap in ufs will be a crude determinant of the type cap to use. You won;t see any 10uf micas or ceramics, and you won;t find 120pf e-caps.

Where they overlap, would a 120pf mica sound better than a ceramic? Probably. Or would a 1uf filn cap sound better than a 1uf e-cap? Probably.

Tantalum caps are extremely sensitive to reverse voltage - they won;t tolerate it at all. E-caps will survive momentary reversals often times. But IN GENERAL if you cover the basic voltage and capacitance and mind polarity on polarized caps, you can interchange them. Not saying you'd want to, mind you.

And for that matter, you can always use non-polar electrolytics. I have a draw of various values of those here too.

[nopainkiller]

wha- but I thought I did say that.

[nopainkiller]

I wasn't too clear, I meant you could take out an existing flim cap and put in an e cap. You would need to follow polarity tho. The other way around, and it wouldn't matter since film caps can go either way. Also forgot that tants were polarized.

I dunno why I even posted that first post. It doesn't make any sense.